[RFC PATCH 2/5] Revert soft limit reclaim implementation in memcg.

[Ying Han <yinghan@google.com>]

This reverts the soft limit reclaim implementation (RB-tree based) merged
in 2.6.32 kernel.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Ying Han <yinghan@google.com>
---
 include/linux/memcontrol.h |    9 -
 include/linux/swap.h       |    4 -
 mm/memcontrol.c            |  423 --------------------------------------------
 mm/vmscan.c                |   43 -----
 4 files changed, 0 insertions(+), 479 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 7c1450c..ca5a18d 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -146,8 +146,6 @@ static inline void mem_cgroup_dec_page_stat(struct page *page,
 	mem_cgroup_update_page_stat(page, idx, -1);
 }
 
-unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order,
-						gfp_t gfp_mask);
 u64 mem_cgroup_get_limit(struct mem_cgroup *mem);
 
 void mem_cgroup_count_vm_event(struct mm_struct *mm, enum vm_event_item idx);
@@ -359,13 +357,6 @@ static inline void mem_cgroup_dec_page_stat(struct page *page,
 }
 
 static inline
-unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order,
-					    gfp_t gfp_mask);
-{
-	return 0;
-}
-
-static inline
 u64 mem_cgroup_get_limit(struct mem_cgroup *mem)
 {
 	return 0;
diff --git a/include/linux/swap.h b/include/linux/swap.h
index a5c6da5..885cf19 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -254,10 +254,6 @@ extern unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
 extern unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *mem,
 						  gfp_t gfp_mask, bool noswap,
 						  unsigned int swappiness);
-extern unsigned long mem_cgroup_shrink_node_zone(struct mem_cgroup *mem,
-						gfp_t gfp_mask, bool noswap,
-						unsigned int swappiness,
-						struct zone *zone);
 extern int __isolate_lru_page(struct page *page, int mode, int file);
 extern unsigned long shrink_all_memory(unsigned long nr_pages);
 extern int vm_swappiness;
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index c98ad1b..5228039 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -34,7 +34,6 @@
 #include <linux/rcupdate.h>
 #include <linux/limits.h>
 #include <linux/mutex.h>
-#include <linux/rbtree.h>
 #include <linux/slab.h>
 #include <linux/swap.h>
 #include <linux/swapops.h>
@@ -149,12 +148,6 @@ struct mem_cgroup_per_zone {
 	unsigned long		count[NR_LRU_LISTS];
 
 	struct zone_reclaim_stat reclaim_stat;
-	struct rb_node		tree_node;	/* RB tree node */
-	unsigned long long	usage_in_excess;/* Set to the value by which */
-						/* the soft limit is exceeded*/
-	bool			on_tree;
-	struct mem_cgroup	*mem;		/* Back pointer, we cannot */
-						/* use container_of	   */
 };
 /* Macro for accessing counter */
 #define MEM_CGROUP_ZSTAT(mz, idx)	((mz)->count[(idx)])
@@ -167,26 +160,6 @@ struct mem_cgroup_lru_info {
 	struct mem_cgroup_per_node *nodeinfo[MAX_NUMNODES];
 };
 
-/*
- * Cgroups above their limits are maintained in a RB-Tree, independent of
- * their hierarchy representation
- */
-
-struct mem_cgroup_tree_per_zone {
-	struct rb_root rb_root;
-	spinlock_t lock;
-};
-
-struct mem_cgroup_tree_per_node {
-	struct mem_cgroup_tree_per_zone rb_tree_per_zone[MAX_NR_ZONES];
-};
-
-struct mem_cgroup_tree {
-	struct mem_cgroup_tree_per_node *rb_tree_per_node[MAX_NUMNODES];
-};
-
-static struct mem_cgroup_tree soft_limit_tree __read_mostly;
-
 struct mem_cgroup_threshold {
 	struct eventfd_ctx *eventfd;
 	u64 threshold;
@@ -339,12 +312,7 @@ static bool move_file(void)
 					&mc.to->move_charge_at_immigrate);
 }
 
-/*
- * Maximum loops in reclaim, used for soft limit reclaim to prevent
- * infinite loops, if they ever occur.
- */
 #define	MEM_CGROUP_MAX_RECLAIM_LOOPS		(100)
-#define	MEM_CGROUP_MAX_SOFT_LIMIT_RECLAIM_LOOPS	(2)
 
 enum charge_type {
 	MEM_CGROUP_CHARGE_TYPE_CACHE = 0,
@@ -401,164 +369,6 @@ page_cgroup_zoneinfo(struct mem_cgroup *mem, struct page *page)
 	return mem_cgroup_zoneinfo(mem, nid, zid);
 }
 
-static struct mem_cgroup_tree_per_zone *
-soft_limit_tree_node_zone(int nid, int zid)
-{
-	return &soft_limit_tree.rb_tree_per_node[nid]->rb_tree_per_zone[zid];
-}
-
-static struct mem_cgroup_tree_per_zone *
-soft_limit_tree_from_page(struct page *page)
-{
-	int nid = page_to_nid(page);
-	int zid = page_zonenum(page);
-
-	return &soft_limit_tree.rb_tree_per_node[nid]->rb_tree_per_zone[zid];
-}
-
-static void
-__mem_cgroup_insert_exceeded(struct mem_cgroup *mem,
-				struct mem_cgroup_per_zone *mz,
-				struct mem_cgroup_tree_per_zone *mctz,
-				unsigned long long new_usage_in_excess)
-{
-	struct rb_node **p = &mctz->rb_root.rb_node;
-	struct rb_node *parent = NULL;
-	struct mem_cgroup_per_zone *mz_node;
-
-	if (mz->on_tree)
-		return;
-
-	mz->usage_in_excess = new_usage_in_excess;
-	if (!mz->usage_in_excess)
-		return;
-	while (*p) {
-		parent = *p;
-		mz_node = rb_entry(parent, struct mem_cgroup_per_zone,
-					tree_node);
-		if (mz->usage_in_excess < mz_node->usage_in_excess)
-			p = &(*p)->rb_left;
-		/*
-		 * We can't avoid mem cgroups that are over their soft
-		 * limit by the same amount
-		 */
-		else if (mz->usage_in_excess >= mz_node->usage_in_excess)
-			p = &(*p)->rb_right;
-	}
-	rb_link_node(&mz->tree_node, parent, p);
-	rb_insert_color(&mz->tree_node, &mctz->rb_root);
-	mz->on_tree = true;
-}
-
-static void
-__mem_cgroup_remove_exceeded(struct mem_cgroup *mem,
-				struct mem_cgroup_per_zone *mz,
-				struct mem_cgroup_tree_per_zone *mctz)
-{
-	if (!mz->on_tree)
-		return;
-	rb_erase(&mz->tree_node, &mctz->rb_root);
-	mz->on_tree = false;
-}
-
-static void
-mem_cgroup_remove_exceeded(struct mem_cgroup *mem,
-				struct mem_cgroup_per_zone *mz,
-				struct mem_cgroup_tree_per_zone *mctz)
-{
-	spin_lock(&mctz->lock);
-	__mem_cgroup_remove_exceeded(mem, mz, mctz);
-	spin_unlock(&mctz->lock);
-}
-
-
-static void mem_cgroup_update_tree(struct mem_cgroup *mem, struct page *page)
-{
-	unsigned long long excess;
-	struct mem_cgroup_per_zone *mz;
-	struct mem_cgroup_tree_per_zone *mctz;
-	int nid = page_to_nid(page);
-	int zid = page_zonenum(page);
-	mctz = soft_limit_tree_from_page(page);
-
-	/*
-	 * Necessary to update all ancestors when hierarchy is used.
-	 * because their event counter is not touched.
-	 */
-	for (; mem; mem = parent_mem_cgroup(mem)) {
-		mz = mem_cgroup_zoneinfo(mem, nid, zid);
-		excess = res_counter_soft_limit_excess(&mem->res);
-		/*
-		 * We have to update the tree if mz is on RB-tree or
-		 * mem is over its softlimit.
-		 */
-		if (excess || mz->on_tree) {
-			spin_lock(&mctz->lock);
-			/* if on-tree, remove it */
-			if (mz->on_tree)
-				__mem_cgroup_remove_exceeded(mem, mz, mctz);
-			/*
-			 * Insert again. mz->usage_in_excess will be updated.
-			 * If excess is 0, no tree ops.
-			 */
-			__mem_cgroup_insert_exceeded(mem, mz, mctz, excess);
-			spin_unlock(&mctz->lock);
-		}
-	}
-}
-
-static void mem_cgroup_remove_from_trees(struct mem_cgroup *mem)
-{
-	int node, zone;
-	struct mem_cgroup_per_zone *mz;
-	struct mem_cgroup_tree_per_zone *mctz;
-
-	for_each_node_state(node, N_POSSIBLE) {
-		for (zone = 0; zone < MAX_NR_ZONES; zone++) {
-			mz = mem_cgroup_zoneinfo(mem, node, zone);
-			mctz = soft_limit_tree_node_zone(node, zone);
-			mem_cgroup_remove_exceeded(mem, mz, mctz);
-		}
-	}
-}
-
-static struct mem_cgroup_per_zone *
-__mem_cgroup_largest_soft_limit_node(struct mem_cgroup_tree_per_zone *mctz)
-{
-	struct rb_node *rightmost = NULL;
-	struct mem_cgroup_per_zone *mz;
-
-retry:
-	mz = NULL;
-	rightmost = rb_last(&mctz->rb_root);
-	if (!rightmost)
-		goto done;		/* Nothing to reclaim from */
-
-	mz = rb_entry(rightmost, struct mem_cgroup_per_zone, tree_node);
-	/*
-	 * Remove the node now but someone else can add it back,
-	 * we will to add it back at the end of reclaim to its correct
-	 * position in the tree.
-	 */
-	__mem_cgroup_remove_exceeded(mz->mem, mz, mctz);
-	if (!res_counter_soft_limit_excess(&mz->mem->res) ||
-		!css_tryget(&mz->mem->css))
-		goto retry;
-done:
-	return mz;
-}
-
-static struct mem_cgroup_per_zone *
-mem_cgroup_largest_soft_limit_node(struct mem_cgroup_tree_per_zone *mctz)
-{
-	struct mem_cgroup_per_zone *mz;
-
-	spin_lock(&mctz->lock);
-	mz = __mem_cgroup_largest_soft_limit_node(mctz);
-	spin_unlock(&mctz->lock);
-	return mz;
-}
-
 /*
  * Implementation Note: reading percpu statistics for memcg.
  *
@@ -596,15 +406,6 @@ static long mem_cgroup_read_stat(struct mem_cgroup *mem,
 	return val;
 }
 
-static long mem_cgroup_local_usage(struct mem_cgroup *mem)
-{
-	long ret;
-
-	ret = mem_cgroup_read_stat(mem, MEM_CGROUP_STAT_RSS);
-	ret += mem_cgroup_read_stat(mem, MEM_CGROUP_STAT_CACHE);
-	return ret;
-}
-
 static void mem_cgroup_swap_statistics(struct mem_cgroup *mem,
 					 bool charge)
 {
@@ -768,7 +569,6 @@ static void memcg_check_events(struct mem_cgroup *mem, struct page *page)
 		__mem_cgroup_target_update(mem, MEM_CGROUP_TARGET_THRESH);
 		if (unlikely(__memcg_event_check(mem,
 			MEM_CGROUP_TARGET_SOFTLIMIT))){
-			mem_cgroup_update_tree(mem, page);
 			__mem_cgroup_target_update(mem,
 				MEM_CGROUP_TARGET_SOFTLIMIT);
 		}
@@ -1550,43 +1350,6 @@ static unsigned long mem_cgroup_reclaim(struct mem_cgroup *mem,
 	return total;
 }
 
-/*
- * Visit the first child (need not be the first child as per the ordering
- * of the cgroup list, since we track last_scanned_child) of @mem and use
- * that to reclaim free pages from.
- */
-static struct mem_cgroup *
-mem_cgroup_select_victim(struct mem_cgroup *root_mem)
-{
-	struct mem_cgroup *ret = NULL;
-	struct cgroup_subsys_state *css;
-	int nextid, found;
-
-	if (!root_mem->use_hierarchy) {
-		css_get(&root_mem->css);
-		ret = root_mem;
-	}
-
-	while (!ret) {
-		rcu_read_lock();
-		nextid = root_mem->last_scanned_child + 1;
-		css = css_get_next(&mem_cgroup_subsys, nextid, &root_mem->css,
-				   &found);
-		if (css && css_tryget(css))
-			ret = container_of(css, struct mem_cgroup, css);
-
-		rcu_read_unlock();
-		/* Updates scanning parameter */
-		if (!css) {
-			/* this means start scan from ID:1 */
-			root_mem->last_scanned_child = 0;
-		} else
-			root_mem->last_scanned_child = found;
-	}
-
-	return ret;
-}
-
 #if MAX_NUMNODES > 1
 
 /*
@@ -1662,71 +1425,6 @@ int mem_cgroup_select_victim_node(struct mem_cgroup *mem)
 }
 #endif
 
-static int mem_cgroup_soft_reclaim(struct mem_cgroup *root_mem,
-					struct zone *zone,
-					gfp_t gfp_mask)
-{
-	struct mem_cgroup *victim;
-	int ret, total = 0;
-	int loop = 0;
-	bool noswap = false;
-	bool is_kswapd = false;
-	unsigned long excess;
-
-	excess = res_counter_soft_limit_excess(&root_mem->res) >> PAGE_SHIFT;
-
-	/* If memsw_is_minimum==1, swap-out is of-no-use. */
-	if (root_mem->memsw_is_minimum)
-		noswap = true;
-
-	if (current_is_kswapd())
-		is_kswapd = true;
-
-	while (1) {
-		victim = mem_cgroup_select_victim(root_mem);
-		if (victim == root_mem) {
-			loop++;
-			if (loop >= 1)
-				drain_all_stock_async(root_mem);
-			if (loop >= 2) {
-				/*
-				 * If we have not been able to reclaim
-				 * anything, it might because there are
-				 * no reclaimable pages under this hierarchy
-				 */
-				if (!total) {
-					css_put(&victim->css);
-					break;
-				}
-				/*
-				 * We want to do more targeted reclaim.
-				 * excess >> 2 is not to excessive so as to
-				 * reclaim too much, nor too less that we keep
-				 * coming back to reclaim from this cgroup
-				 */
-				if (total >= (excess >> 2) ||
-					(loop > MEM_CGROUP_MAX_RECLAIM_LOOPS)) {
-					css_put(&victim->css);
-					break;
-				}
-			}
-		}
-		if (!mem_cgroup_local_usage(victim)) {
-			/* this cgroup's local usage == 0 */
-			css_put(&victim->css);
-			continue;
-		}
-		/* we use swappiness of local cgroup */
-		ret = mem_cgroup_shrink_node_zone(victim, gfp_mask, noswap,
-						  get_swappiness(victim), zone);
-		css_put(&victim->css);
-		total += ret;
-		if (!res_counter_soft_limit_excess(&root_mem->res))
-			return total;
-	}
-	return total;
-}
-
 /*
  * Check OOM-Killer is already running under our hierarchy.
  * If someone is running, return false.
@@ -2443,8 +2141,6 @@ static void __mem_cgroup_commit_charge(struct mem_cgroup *mem,
 	unlock_page_cgroup(pc);
 	/*
 	 * "charge_statistics" updated event counter. Then, check it.
-	 * Insert ancestor (and ancestor's ancestors), to softlimit RB-tree.
-	 * if they exceeds softlimit.
 	 */
 	memcg_check_events(mem, page);
 }
@@ -3523,94 +3219,6 @@ static int mem_cgroup_resize_memsw_limit(struct mem_cgroup *memcg,
 	return ret;
 }
 
-unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order,
-					    gfp_t gfp_mask)
-{
-	unsigned long nr_reclaimed = 0;
-	struct mem_cgroup_per_zone *mz, *next_mz = NULL;
-	unsigned long reclaimed;
-	int loop = 0;
-	struct mem_cgroup_tree_per_zone *mctz;
-	unsigned long long excess;
-
-	if (order > 0)
-		return 0;
-
-	mctz = soft_limit_tree_node_zone(zone_to_nid(zone), zone_idx(zone));
-	/*
-	 * This loop can run a while, specially if mem_cgroup's continuously
-	 * keep exceeding their soft limit and putting the system under
-	 * pressure
-	 */
-	do {
-		if (next_mz)
-			mz = next_mz;
-		else
-			mz = mem_cgroup_largest_soft_limit_node(mctz);
-		if (!mz)
-			break;
-
-		reclaimed = mem_cgroup_soft_reclaim(mz->mem, zone, gfp_mask);
-		nr_reclaimed += reclaimed;
-
-		spin_lock(&mctz->lock);
-
-		/*
-		 * If we failed to reclaim anything from this memory cgroup
-		 * it is time to move on to the next cgroup
-		 */
-		next_mz = NULL;
-		if (!reclaimed) {
-			do {
-				/*
-				 * Loop until we find yet another one.
-				 *
-				 * By the time we get the soft_limit lock
-				 * again, someone might have aded the
-				 * group back on the RB tree. Iterate to
-				 * make sure we get a different mem.
-				 * mem_cgroup_largest_soft_limit_node returns
-				 * NULL if no other cgroup is present on
-				 * the tree
-				 */
-				next_mz =
-				__mem_cgroup_largest_soft_limit_node(mctz);
-				if (next_mz == mz)
-					css_put(&next_mz->mem->css);
-				else /* next_mz == NULL or other memcg */
-					break;
-			} while (1);
-		}
-		__mem_cgroup_remove_exceeded(mz->mem, mz, mctz);
-		excess = res_counter_soft_limit_excess(&mz->mem->res);
-		/*
-		 * One school of thought says that we should not add
-		 * back the node to the tree if reclaim returns 0.
-		 * But our reclaim could return 0, simply because due
-		 * to priority we are exposing a smaller subset of
-		 * memory to reclaim from. Consider this as a longer
-		 * term TODO.
-		 */
-		/* If excess == 0, no tree ops */
-		__mem_cgroup_insert_exceeded(mz->mem, mz, mctz, excess);
-		spin_unlock(&mctz->lock);
-		css_put(&mz->mem->css);
-		loop++;
-		/*
-		 * Could not reclaim anything and there are no more
-		 * mem cgroups to try or we seem to be looping without
-		 * reclaiming anything.
-		 */
-		if (!nr_reclaimed &&
-			(next_mz == NULL ||
-			loop > MEM_CGROUP_MAX_SOFT_LIMIT_RECLAIM_LOOPS))
-			break;
-	} while (!nr_reclaimed);
-	if (next_mz)
-		css_put(&next_mz->mem->css);
-	return nr_reclaimed;
-}
-
 /*
  * This routine traverse page_cgroup in given list and drop them all.
  * *And* this routine doesn't reclaim page itself, just removes page_cgroup.
@@ -4705,9 +4313,6 @@ static int alloc_mem_cgroup_per_zone_info(struct mem_cgroup *mem, int node)
 		mz = &pn->zoneinfo[zone];
 		for_each_lru(l)
 			INIT_LIST_HEAD(&mz->lruvec.lists[l]);
-		mz->usage_in_excess = 0;
-		mz->on_tree = false;
-		mz->mem = mem;
 	}
 	return 0;
 }
@@ -4760,7 +4365,6 @@ static void __mem_cgroup_free(struct mem_cgroup *mem)
 {
 	int node;
 
-	mem_cgroup_remove_from_trees(mem);
 	free_css_id(&mem_cgroup_subsys, &mem->css);
 
 	for_each_node_state(node, N_POSSIBLE)
@@ -4815,31 +4419,6 @@ static void __init enable_swap_cgroup(void)
 }
 #endif
 
-static int mem_cgroup_soft_limit_tree_init(void)
-{
-	struct mem_cgroup_tree_per_node *rtpn;
-	struct mem_cgroup_tree_per_zone *rtpz;
-	int tmp, node, zone;
-
-	for_each_node_state(node, N_POSSIBLE) {
-		tmp = node;
-		if (!node_state(node, N_NORMAL_MEMORY))
-			tmp = -1;
-		rtpn = kzalloc_node(sizeof(*rtpn), GFP_KERNEL, tmp);
-		if (!rtpn)
-			return 1;
-
-		soft_limit_tree.rb_tree_per_node[node] = rtpn;
-
-		for (zone = 0; zone < MAX_NR_ZONES; zone++) {
-			rtpz = &rtpn->rb_tree_per_zone[zone];
-			rtpz->rb_root = RB_ROOT;
-			spin_lock_init(&rtpz->lock);
-		}
-	}
-	return 0;
-}
-
 static struct cgroup_subsys_state * __ref
 mem_cgroup_create(struct cgroup_subsys *ss, struct cgroup *cont)
 {
@@ -4861,8 +4440,6 @@ mem_cgroup_create(struct cgroup_subsys *ss, struct cgroup *cont)
 		enable_swap_cgroup();
 		parent = NULL;
 		root_mem_cgroup = mem;
-		if (mem_cgroup_soft_limit_tree_init())
-			goto free_out;
 		for_each_possible_cpu(cpu) {
 			struct memcg_stock_pcp *stock =
 						&per_cpu(memcg_stock, cpu);
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 7c9ed8e..d9376d1 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2218,43 +2218,6 @@ unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
 
 #ifdef CONFIG_CGROUP_MEM_RES_CTLR
 
-unsigned long mem_cgroup_shrink_node_zone(struct mem_cgroup *mem,
-						gfp_t gfp_mask, bool noswap,
-						unsigned int swappiness,
-						struct zone *zone)
-{
-	struct scan_control sc = {
-		.nr_to_reclaim = SWAP_CLUSTER_MAX,
-		.may_writepage = !laptop_mode,
-		.may_unmap = 1,
-		.may_swap = !noswap,
-		.swappiness = swappiness,
-		.order = 0,
-		.target_mem_cgroup = mem,
-		.mem_cgroup = mem,
-	};
-
-	sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
-			(GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK);
-
-	trace_mm_vmscan_memcg_softlimit_reclaim_begin(0,
-						      sc.may_writepage,
-						      sc.gfp_mask);
-
-	/*
-	 * NOTE: Although we can get the priority field, using it
-	 * here is not a good idea, since it limits the pages we can scan.
-	 * if we don't reclaim here, the shrink_zone from balance_pgdat
-	 * will pick up pages from other mem cgroup's as well. We hack
-	 * the priority and make it zero.
-	 */
-	do_shrink_zone(0, zone, &sc);
-
-	trace_mm_vmscan_memcg_softlimit_reclaim_end(sc.nr_reclaimed);
-
-	return sc.nr_reclaimed;
-}
-
 unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *mem_cont,
 					   gfp_t gfp_mask,
 					   bool noswap,
@@ -2500,12 +2463,6 @@ loop_again:
 			sc.nr_scanned = 0;
 
 			/*
-			 * Call soft limit reclaim before calling shrink_zone.
-			 */
-			mem_cgroup_soft_limit_reclaim(zone, order,
-					sc.gfp_mask);
-
-			/*
 			 * We put equal pressure on every zone, unless
 			 * one zone has way too many pages free
 			 * already. The "too many pages" is defined
-- 
1.7.3.1

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